Backlight unit

ABSTRACT

Provided is a backlight unit including a plurality of light emitting diodes (LEDs) that emit light; a plurality of LED modules having a printed circuit board (PCB) which supports and drives the plurality of LEDs; a plurality of optical sheets that are attached to the top surfaces of the respective LED modules; and a plurality of heat radiating pads that are attached to the rear surfaces of the respective LED modules.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application Nos.10-2007-0072266 and 10-2008-0069033 filed with the Korea IntellectualProperty Office on Jul. 19, 2007 and Jul. 16, 2008, the disclosure ofwhich is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a backlight unit which uses lightemitting diode (LED) modules.

2. Description of the Related Art

Recently, with the rapid development of semiconductor technology, theperformance of products is further enhanced while the size and weightthereof is reduced. Cathode ray tubes (CRT), which are still used forinformation display devices, have many advantages in terms ofperformance and price, but have a limit in miniaturization andportability. As a device for overcoming such a disadvantage, a liquidcrystal display (LCD) device has been proposed. Since the LCD device canbe reduced in size and weight and has low power consumption, the LCDdevice is being recognized as a substitute which can overcome thedisadvantages of CRT. Currently, almost every information processingequipment requiring a display device includes the LCD device mountedthereon.

In the LCD device, a voltage is applied to a specific moleculararrangement of liquid crystal such that the molecular arrangement isconverted into another molecular arrangement, and changes in opticalcharacteristics of a liquid crystal cell, which emits light through theconverted molecular arrangement, such as birefringence, rotatory power,two-color property, and diffusion, are converted into visual changes.That is, the LCD device is such a display device that uses themodulation of light by the liquid crystal cell.

Since the LCD device is a passive element which cannot emit light foritself, a backlight unit attached to the rear surface of a liquidcrystal panel is used to illuminate the liquid crystal panel. The lighttransmittance of the liquid crystal panel is adjusted by an appliedelectrical signal, and still or moving images are displayed on theliquid crystal panel.

As for a lamp used in the backlight unit which supplies light to theliquid crystal panel, a cold cathode fluorescent lamp (CCFL) has beenwidely used. Recently, however, a backlight unit using LEDs arefrequently used for a variety of display devices such as a portabledevice and a field sequential color LCD device.

Referring to FIG. 1, a conventional backlight unit using LEDs will bedescribed in detail.

FIG. 1 is a perspective view of a conventional backlight unit.

As shown in FIG. 1, the conventional backlight unit is positioned undera display panel (not shown) and includes a plurality of LEDs 110, aplurality of LED modules 120 having a printed circuit board (PCB) whichsupports and drives the plurality of LEDs 110, an optical sheet 140which is provided above the plurality of LED modules 120 so as to bespaced at a predetermined distance from the LED modules 120, and a heatradiating pad 130 which is provided on the rear surface of the LEDmodules 120.

The conventional backlight unit is constructed in such a manner that theoptical sheet 140 disposed above the plurality of LED modules 120 isspaced at a predetermined distance from the LED modules 120, and oneoptical sheet 140 covers all the LED modules 120. In this case, the heatradiating pad 130 on the rear surface of the LED modules 180 may bedivided in accordance with the number of LED modules 120 so as to beindividually attached to each of the LED modules 120, or one heatradiating pad 130 may be attached so as to cover the overall LED modules120.

However, when the optical sheet of the backlight unit is formed so as tobe spaced from the LED modules, there are difficulties in achieving areduction in size and thickness of a display device using the backlightunit.

Further, when the optical sheet for controlling light orientation isreceived and fixed as one sheet which covers the overall LED modules,the optical sheet above the LED modules should be entirely removed ifany one of the LED modules is damaged. Therefore, a rework process ofthe backlight unit becomes complicated.

SUMMARY OF THE INVENTION

An advantage of the present invention is that it provides a backlightunit in which an LED module, an optical sheet positioned above the LEDmodule, and a heat radiating pad positioned under the LED module areintegrally formed, thereby reducing the size and thickness of thebacklight unit.

Additional aspects and advantages of the present general inventiveconcept will be set forth in part in the description which follows and,in part, will be obvious from the description, or may be learned bypractice of the general inventive concept.

According to an aspect of the invention, a backlight unit comprises aplurality of light emitting diodes (LEDs) that emit light; a pluralityof LED modules having a printed circuit board (PCB) which supports anddrives the plurality of LEDs; a plurality of optical sheets that areattached to the top surfaces of the respective LED modules; and aplurality of heat radiating pads that are attached to the rear surfacesof the respective LED modules.

The optical sheet, and the heat radiating pad may be formed to have thesame size.

The optical sheet and the heat radiating pad may have a smaller sizethan the LED module.

The LED modules may be arranged in parallel to each other in thelongitudinal direction thereof.

The LED modules may be arranged so as to surround a predeterminedregion.

The plurality of LEDs may be continuously arranged in a triangle orrectangle shape.

The plurality of LEDs may be separated for each block in a circuitmanner such that some LEDs among the plurality of LEDs can be partiallyturned on/off.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects and advantages of the present generalinventive concept will become apparent and more readily appreciated fromthe following description of the embodiments, taken in conjunction withthe accompanying drawings of which:

FIG. 1 is a perspective view of a conventional backlight unit;

FIG. 2 is a perspective view of a backlight unit according to theinvention;

FIG. 3 is a perspective view showing the arrangement of a plurality ofLEDs in a backlight unit according to a first embodiment of theinvention;

FIG. 4 is a plan view showing the arrangement of a plurality of blocksin a backlight unit according to a second embodiment of the invention;

FIG. 5 is a plan view showing the arrangement of a plurality of LEDs inthe backlight unit according to the second embodiment of the invention;

FIG. 6 is a plan view showing the arrangement of a plurality of blocksin a backlight unit according to a third embodiment of the invention;

FIG. 7 is a plan view showing the arrangement of a plurality of LEDs inthe backlight unit according to the third embodiment of the invention;

FIG. 8 is an image showing the brightness of the backlight unitaccording to the invention;

FIG. 9 is a plan view of the backlight unit according to the invention;

FIG. 10 is a circuit diagram of the backlight unit according to theinvention; and

FIG. 11 is a perspective view showing another example for thearrangement of LED modules in the backlight unit according to theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the embodiments of the presentgeneral inventive concept, examples of which are illustrated in theaccompanying drawings, wherein like reference numerals refer to likeelements throughout. The embodiments are described below in order toexplain the present general inventive concept by referring to thefigures.

Hereinafter, a backlight unit according to the present invention will bedescribed in detail with reference to the accompanying drawings.

FIG. 2 is a perspective view of a backlight unit according to anembodiment of the invention.

As shown in FIG. 2, the backlight unit 100 according to the embodimentof the invention is positioned under a display device (not shown) andincludes a plurality of LEDs 110 which emit light, a plurality of LEDmodules 120 having a printed circuit board (PCB) which supports anddrives the plurality of LEDs 110, a plurality of optical sheets 140which are attached to the top surfaces of the respective LED modules120, and a plurality of heat radiating pads 130 which are attached tothe rear surfaces of the respective LED modules 120.

The plurality of LEDs 110 can implement white light. For example, theplurality of LEDs 110 may include blue LED chips and red and greenphosphors disposed on the blue LED chips. Alternately, the plurality ofLEDs 110 may include blue LED chips, red LED chips, and green LED chips.In this case, the blue LED chips include LED chips having an emissionwavelength of 250 to 420 nm and blue phosphors disposed on the LEDchips. Further, the red and green LED chips include LED respectivelyinclude red and green phosphors disposed on LED chips having an emissionwavelength of 250 to 420 nm.

As for a material used as the red phosphor, nitride-based CaAlSiN₃:Eu,sulfide-based (Ca, Sr)S:Eu and so on may be exemplified.

As for a material used as the green phosphor, silicate-based A₂SiO₄having a composition of 2, 1, 4, silicate-based A₃SiO₅ having acomposition of 3,1,5, sulfide-based SrGa₂S₄:Eu, and nitride-basedBeta-SiAlON may be exemplified. As for the silicate-based phosphorhaving a composition of 2, 1, 4, (Sr,Ba,Ca,Mg)2SiO4:Eu,X may be used. Inthis case, Sr is an essential element, and Ba, Ca, and Mg may beselectively included (0≦Ba,Ca,Mg≦1), if necessary. Eu is used as anactivator, and Eu2+ is used. X is an additive and may include at leastone or more of Ho, Er, Ce, Y, F, Cl, Br, I, P, S, N, and Gd. A dopingamount of X may be adjusted in the range of 1 to 500000 ppm. Further, asfor the silicate-based phosphor having a composition of 3,1,5,(Sr,Ba,C,Mg)3SiO5:Eu,X may be used. In this case, Sr is an essentialelement, and Ba, Ca, and Mg may be selectively included (0≦Ba,Ca,Mg≦1),if necessary. Eu is used as an activator, and Eu2+ is used. X is anadditive and may include at least one or more of Ho, Er, Ce, Y, F, Cl,Br, I, P, S, N, and Gd. A doping amount of X may be adjusted in therange of 1 to 500000 ppm.

As for a material used as the blue phosphor, a silicate-based material,a sulfide-based material, a nitride-based material, and analuminate-based material may be exemplified.

The plurality of LED modules 120 include a plurality of LEDs 110arranged in a matrix shape composed of m rows and n columns. In thiscase, the plurality of LEDs 110 arranged in a m×n matrix may be dividedinto a plurality of blocks. Here, m and n are positive numbers equal toor more than 2.

Each of the LED modules 120 includes a plurality of blocks. In thiscase, the plurality of LEDs 110 may be divided for each block so as tobe separately driven.

As such, the backlight unit 100 can be divided and driven for eachblock.

Further, as any one of the number of LED modules, the number of blocksincluded in the LED module, and the number of LED chips for each blockis properly adjusted, luminous intensity required for the backlight unitcan be properly adjusted.

Specifically, the selection of the proper number of LEDs, the number ofLED modules, the number of blocks for each LED module, and the number ofLED chips for each block depending on the size of the backlight unitwill be described.

In this embodiment, backlight units having a size of 40, 46, 52, and 57inches, respectively, are exemplified.

First, the total luminous intensity (lumens) required for each backlightunit size may be set to 7000, 8000, 93000, and 13000. The number of LEDchips which can satisfy the total luminous intensity can be determineddepending on the luminous intensity of a unit LED, as shown in Table 1.

In general, 4, 8, 10, and 15 lumens LEDs are used. Table 1 shows thenumber of LEDs required for each backlight unit size.

TABLE 1 Backlight unit size (inch) 40 46 52 57 Total luminous intensity(lumens) 7000 8000 9300 13000 Number of LEDs  4 lumens LED 1750 20002325 3250 depending on luminous  8 lumens LED 875 1000 1162 1625intensity of unit LED 10 lumens LED 700 800 930 1300 15 lumens LED 466533 622 866

As shown in Table 1, the number of LEDs required depending on theluminous intensity of the unit LED may slightly differ. Such a largenumber of LEDs need to be properly arranged in consideration of coloruniformity and brightness, so as to have optical density.

To easily implement the arrangement for the area and number, the numberof LED modules, the number of blocks for each module, and the number ofLEDs for each block are properly selected so as to obtain optimalbrightness and color uniformity.

To satisfy the condition shown in Table 1, the number of LED modules,the number of blocks for each module, and the number of LEDs for eachblock in each backlight unit size may be selected as shown in Table 2.

TABLE 2 Backlight unit size (inch) 40 46 52 57 Number of LEDs 466-1750533-2000 622-2325 866-3250 Number of LED modules 6-12 6-12 6-12 6-20Number of blocks for 4-14 5-15 6-28 6-28 each module Number of LEDs for6-24 6-24 6-24 6-24 each block

In the case of 40 inch and 46 inch corresponding to the middle size, thenumber of LED modules and the number of LEDs for each block can beselected in the same range. In the case of 40 inch, the backlight unitmay be constructed in such a manner that the LED module is divided into4-14 blocks. In the case of 46 inch, the backlight unit may beconstructed in such a manner that the LED module is divided into 5-15blocks. If necessary, the number of modules and the number of LEDs foreach block may be properly selected within the range shown in Table 2.

In the case of 52 inch and 57 inch corresponding to the large size, thenumber of blocks for each module may be selected in the range of 6-28,and the number of LEDs for each block may be selected in the range of6-24. Preferably, in the case of 52 inch, the number of LED modules maybe selected in the range of 6-12. In the case of 57 inch, the number ofLED modules may be selected in the range of 6-20.

That is, the number of LED modules may be selected in the range of 2-28,and each of the modules may be composed of 1 to 28 blocks. Further, 2 to240 LEDs may be arranged in each of the blocks.

In this embodiment, the number of LED modules, the number of blocks, andthe number of LEDs are not limited thereto.

Each of the optical sheets 140 has a plurality of light transmissionholes (not shown) corresponding to the respective LEDs 100, and servesto diffuse or reflect incident light in a predetermined direction suchthat light generated from the LEDs 110 can be functionally diffused orirradiated toward the display device.

The optical sheet 140 is formed to have the same size of one LED module120 among the plurality of LED modules 120, and is individually attachedto each of the LED modules 120.

Accordingly, the optical sheet 140 and the LED module 120 can beintegrally formed, which makes it possible to reduce the size andthickness of the backlight unit 100.

It has been described in this embodiment that the sizes of the opticalsheet 140 and the heat radiating pad 130 are equal to that of the LEDmodule. Without being limited thereto, the sizes of the optical sheet140 and the heat radiating pad 130 may be smaller than that of the LEDmodule.

Since the optical sheet 140 is individually attached to each of the LEDmodules 120, only the optical sheet 140 attached to a damaged LED module120 among the plurality of LED modules 120 is selectively removed so asto replace or repair the damaged LED module 120, which makes it possibleto facilitate the subsequent process such as the rework process of thebacklight unit 100.

The heat radiating pad 130 serves to radiate heat generated from the LEDmodule 120 and may be formed of a heat radiating plate composed ofsynthetic resin or glass or a metal plate with high heat conductivity.If necessary, the heat radiating pad 130 on the bottom surface of theLED module 120 may be removed, in case where a small amount of heat isgenerated.

Further, the number of LED modules having optimal brightness and coloruniformity, the number of blocks for each LED module, and the number ofLEDs can be properly selected, which makes it possible to properlyselect the number of the optical sheets and the heat radiating pads.

The optical sheet 140, the LED module 120, and the heat radiating pad130 are integrally formed, thereby achieving a reduction in size andthickness of the backlight unit 100. Further, the optical sheet 140 isindividually attached on each of the LED modules 120, which makes itpossible to easily rework the backlight unit 100.

In this embodiment, it has been described that the optical sheets 140are separated for each block. Like the optical sheets 140, reflectingsheets may be separated for each block.

As shown in FIG. 2, the plurality of LEDs are arranged in one line onone LED module 120 among the plurality of LED modules 120. Without beinglimited thereto, however, the plurality of LEDs may be arranged invarious shapes depending on the characteristic of the backlight unit.

Hereinafter, a variety of examples for the arrangement of the LEDsdisposed in the LED module 120 will be described with reference thedrawings.

FIG. 3 is a perspective view showing the arrangement of a plurality ofLEDs in a backlight unit according to a first embodiment of theinvention.

As shown in FIG. 3, the plurality of LEDs 110 may be arranged in twolines on one LED module 120. That is, the plurality of LEDs 110 may bearranged in one or more lines on one LED module 120 depending on thecharacteristic of the backlight unit.

FIG. 4 is a plan view showing the arrangement of a plurality of blocksin a backlight unit according to a second embodiment of the invention.

FIG. 5 is a plan view showing the arrangement of a plurality of LEDs inthe backlight unit according to the second embodiment of the invention.

As shown in FIG. 4, a plurality of LEDs 110 may be continuously arrangedon the LED module 120 so as to have a triangle shape. The plurality ofLEDs 110 may be divided into a plurality of blocks A to D such that thebacklight unit 100 is separately driven for each block. The respectiveblocks may be separated from each other so as to be independently turnedon/off, and the LEDs disposed in each block are connected throughcircuit patterns. In this case, the heat radiating pad on the bottomsurface of the LED module 120 may be omitted, if necessary, when a smallamount of heat is generated.

By adjusting the arrangement of the LEDs, the backlight unit 100 canhave optimal uniformity. As shown in FIG. 5, when the LEDs 110implements white light, the LEDs 110 are separated from each other. Inthis case, the center luminous intensity C of an LED unit U composed ofarbitrary LEDs, which are disposed at the shortest distance from eachother, should correspond to 80 to 120% of the average of luminousintensities of the LEDs such that the backlight unit 100 has optimaluniformity.

At this time, a first distance (a) between first and second LEDs 110 aand 110 b, which are disposed in the same column and are adjacent toeach other, may be set in the range of 20 to 140 mm. Further, second andthird distances (b) and (e) between the first and second LEDs 110 a and110 b and a third LED 110 c which is adjacent to the first and secondLEDs in the row direction may be set in the range of 15 to 90 mm. Inthis case, the second and third distances (b) and (e) may be equal toeach other such that the backlight unit 100 has optimal uniformity. Thefirst distance (a) should be larger than the second and third distances(b) and (e).

Further, the distance between the first and third LEDs 110 a and 110 cwhich are adjacent to each other in the column direction and thedistance between the second and third LEDs 110 b and 110 c which areadjacent to each other in the row direction may be set in the range of8.2 to 70 mm.

FIG. 6 is a plan view showing the arrangement of a plurality of blocksin a backlight unit according to a third embodiment of the invention.

FIG. 7 is a plan view showing the arrangement of a plurality of LEDs inthe backlight unit according to the third embodiment of the invention.

As shown in FIG. 6, the plurality of LEDs 110 on the LED module 120 maybe continuously arranged in a square or rectangle, for example. Theplurality of LEDs 110 may be divided into a plurality of blocks A to Dsuch that the backlight unit is separately driven for each block. Therespective blocks may be separated from each other so as to beindependently turned on/off, and the LEDs disposed in each block areconnected through circuit patterns. In this case, the heat radiating padon the bottom surface of the LED module 120 may be omitted, ifnecessary, when a small amount of heat is generated.

As shown in FIG. 7, when the plurality of LEDs are arranged in arectangle, the center luminous intensity C of an LED unit U composed ofarbitrary LEDs, which are disposed at the shortest distance from eachother, should correspond to 80 to 120% of the average of luminousintensities of the LEDs. For this construction, distances D1 and D2between the adjacent LEDs 110 may be set in the range of 8.2 to 70 mm.Further, an angle between the column direction where the LEDs 110 arearranged and the position where the LED is disposed may be formed in therange of 70 to 110 degrees.

In such an LED arrangement, the LEDs should satisfy the followingcondition so as to enhance color reproducibility and brightness.

To implement white light, the LED chip may include a blue LED chiphaving a dominant wavelength of 420-456 nm; red phosphors which aredisposed around the blue LED chip and are excited by the blue LED chipso as to emit red light; and green phosphors which are disposed aroundthe blue LED and are excited by the blue LED chip so as to emit greenlight. In this case, the color coordinates of the red light emitted fromthe red phosphors should be positioned within a region surrounded byfour vertexes of (0.6448, 0.4544), (0.8079, 0.2820), (0.6427, 0.2905)and (0.4794, 0.4633) on the basis of the CIE 1931 color coordinatesystem, and the color coordinates of the green light emitted from thegreen phosphors should be positioned within a region surrounded by fourvertexes of (0.1270, 0.8037), (0.4117, 0.5861), (0.4197, 0.5861), and(0.2555, 0.5030).

Preferably, the FWHM (Full Width at Half-Maximum) of an emissionspectrum of the blue LED chip ranges from 10 to 30 nm, the FWHM of thegreen phosphors ranges from 30 to 100 nm, and the FWHM of the redphosphors ranges from 50 to 200 nm. Accordingly, it is possible toobtain white light with more excellent color uniformity and quality. Inparticular, as the dominant wavelength and the FWHM of the blue LED chipare limited to 420-456 nm and 10-30 nm, respectively, it is possible toenhance the efficiency of CaAlSiN3:Eu red phosphor and(Sr,Ba,Ca,Mg)2SiO4:Eu, X green phosphor (0≦Ba,Ca,Mg≦1).

FIG. 8 is an image showing the brightness of the backlight unitaccording to the invention. As shown in FIG. 8, when the plurality ofLEDs are arranged in such a manner that the center luminous intensity Cof an LED unit U composed of arbitrary LEDs, which are disposed at theshortest distance from each other, corresponds to 80 to 120% of theaverage of luminous intensities of the LEDs, it can be found that thebacklight unit has the optimal uniformity.

In the backlight unit in which the plurality of LED modules each havingthe plurality of LEDs are provided, the uniformity, colorreproducibility, and brightness of the backlight unit can be enhanced byadjusting the shape and arrangement of the LEDs.

Hereinafter, referring to FIGS. 9 and 10, the backlight unit accordingto the invention will be described in more detail.

FIG. 9 is a plan view of the backlight unit according to the invention.

FIG. 10 is a circuit diagram of the backlight unit according to theinvention.

Referring to FIG. 9, the backlight unit 100 according to the inventionmay be a backlight unit which can be separately driven for each block.For example, the backlight unit 100 may include four LED modules 120.Each of the LED modules 120 includes a wiring board 115 and a pluralityof LED chips 110 mounted on the wiring board 115. The LED chips 110 maybe arranged in a matrix composed of 4 rows and 9 columns.

The LED module 120 may be divided into 6 blocks B1 to B6. In thisembodiment, each of the blocks B1 to B6 composing the LED module 120means a unit which can be separately driven.

The LED chips 110 within each of the blocks B1 to B6 may be connected inseries to each other. At least one end of each of the blocks B1 to B6 isconnected to a separate connector such that the LED chips 110 can beseparately driven for each block. To implement the connection, thewiring board 115 of the LED module 120 includes two of first connectors130 and six of second connectors 140 a, 140 b, and 140 c. The first andsecond connectors 130, 140 a, 140 b, and 140 c serve to provide anexternal voltage to the LED chips 110.

On each of the LED modules 120, an optical sheet (not shown) isindividually attached. Therefore, when one LED module 120 among theplurality of LED modules 120 is damaged, only the optical sheet attachedon the damaged LED module 120 can be removed so as to replace or repairthe damaged LED module 120, which makes it possible to easily rework thebacklight unit 100.

Referring to FIG. 10, each of the first to third blocks B1 to B3 iscomposed of six LED chips 110 which are disposed across three columns atthe first and second rows, and each of the fourth to sixth blocks B4 toB6 is composed of six LED chips 110 which are disposed across threecolumns at the third and fourth rows.

The LED chips of each block are connected in series to each other. Inthe series circuit of the first to third blocks B1 to B3, positiveterminals (+) are commonly connected to a first connector P1, andnegative terminals (−) are connected to three of second connectors P21to P23, respectively, for each block. Similarly, in the series circuitof the fourth to six blocks B4 to B6, positive terminals (+) arecommonly connected to the first connector, and negative terminals areconnected to three of second connectors, respectively, for each block.The connectors P1 and P21 to P23 of FIG. 9 may correspond to the firstand second connectors shown in FIG. 8.

As such, the backlight unit according to the invention can implement astructure which is required for the division driving for each block andcan adjust the number of LED chips by the unit of three LED chips.

In the backlight unit according to the invention, the LED chips arearranged in a matrix shape composed a plurality of rows and columns soas to uniformly illuminate light, and the number of LED chips which arerequired for an area can be properly adjusted by adjusting the number ofLED modules, the number of blocks for each LED module, and the number ofLED chips for each block. Therefore, a necessary number of LED chips canbe easily arranged with proper density. As a result, it is possible toeffectively improve a local dimming effect and entire color uniformityin middle- and large-sized displays.

Further, as described above, the optical sheet (not shown) isindividually attached on each of the LED modules 120. Therefore, whenone LED module 120 among the plurality of LED modules 120 is damaged,only the optical sheet attached on the damaged LED module 120 can beremoved so as to replace or repair the damaged LED module 120, whichmakes it possible to easily rework the backlight unit 100.

In this embodiment, it has been described that the LED modules arearranged in the longitudinal direction thereof. However, the arrangementof the LED modules is not limited thereto.

FIG. 11 is a perspective view showing another example for thearrangement of LED modules in the backlight unit according to theinvention.

As shown in FIG. 11, the LED modules 120 may be arranged so as tosurround a predetermined region. In FIG. 11, four LED modules areexemplified, but more than four LED modules are arranged so as tosurround the region. The heat radiating pad on the bottom surface of theLED module maybe omitted, when a small amount of heat is generated.

According to the present invention, the LED module, the optical sheetpositioned on the LED module, and the heat radiating pad positionedunder the LED module are integrally formed, thereby reducing the sizeand thickness of the backlight unit.

Since the optical sheet is individually attached to each of the LEDmodules, only the optical sheet attached to a damaged LED module amongthe plurality of LED modules is selectively removed so as to replace orrepair the damaged LED module, which makes it possible to facilitate thesubsequent process such as the rework process.

Further, as the number of LED modules, the number of blocks for each LEDmodule, and the number of LED for each block are set in consideration ofcolor uniformity and brightness depending on the area of the backlight,it is possible to minimize the number of optical sheets or reflectingsheets.

Accordingly, it is possible to achieve a reduction in size and thicknessof the backlight unit and to enhance a production yield of the backlightunit.

Although a few embodiments of the present general inventive concept havebeen shown and described, it will be appreciated by those skilled in theart that changes may be made in these embodiments without departing fromthe principles and spirit of the general inventive concept, the scope ofwhich is defined in the appended claims and their equivalents.

1. A backlight unit comprising: a plurality of light emitting diodes(LEDs) that emit light; a plurality of LED modules having a printedcircuit board (PCB) which supports and drives the plurality of LEDs; aplurality of optical sheets that are attached to the top surfaces of therespective LED modules; and a plurality of heat radiating pads that areattached to the rear surfaces of the respective LED modules.
 2. Thebacklight unit according to claim 1, wherein the LED module, the opticalsheet, and the heat radiating pad are formed to have the same size. 3.The backlight unit according to claim 1, wherein the optical sheet andthe heat radiating pad have a smaller size than the LED module.
 4. Thebacklight unit according to claim 1, wherein the LED modules arearranged in parallel to each other in the longitudinal directionthereof.
 5. The backlight unit according to claim 1, wherein the LEDmodules are arranged so as to surround a predetermined region.
 6. Thebacklight unit according to claim 1, wherein the plurality of LEDs arecontinuously arranged in a triangle or rectangle shape.
 7. The backlightunit according to claim 1, wherein the plurality of LEDs are separatedfor each block in a circuit manner such that some LEDs among theplurality of LEDs can be partially turned on/off.